We propose a subchannel power control scheme in the OFDM system, which transmits data with a variable power level for each subchannel based on the received SNR. The OFDM system, employing the D-QPSK modulation and the proposed subchannel power control with a grouping coefficient equal to 3, gives about 2.3 dB gain in Eb/N0 comparing with the conventional OFDM system, under the two-ray multipath channel with the mean value of the second-ray's attenuation coefficient equal to 0.25, for the required BER equal to 10-5.

In 1998, Fan and Lei proposed a partially blind signature scheme that could reduce the computation load and the size of the database for electronic cash systems. In this Letter, we show that their scheme could not meet the untraceability property of a blind signature.

This paper deals with a cellular system based on Code Division Multiple Access (CDMA) and investigates the performance of Signal-to-Interference (SIR)-based Closed Loop-Power Control (CLPC) schemes taking into account errors on the feedback channel that conveys the power control command from the base station to the mobile terminals. We have evaluated both the distribution of the received power at the base station and the optimum control step size that minimizes the Control Error (CE) standard deviation, a useful measure of the CLPC performance. The impact of interference variations has been deeply investigated for different mobility scenarios and for different feedback channel error conditions.

This paper discusses the application of a fuzzy-ARTMAP neural network to digital communications channel equalization. This approach provides new solutions for solving the problems, such as complexity and long training, which found when implementing the previously developed neural-basis equalizers. The proposed fuzzy-ARTMAP equalizer is fast and easy to train and includes capabilities not found in other neural network approaches; a small number of parameters, no requirements for the choice of initial weights, automatic increase of hidden units, no risk of getting trapped in local minima, and the capability of adding new data without retraining previously trained data. In simulation studies, binary signals were generated at random in a linear channel with Gaussian noise. The performance of the proposed equalizer is compared with other neural net basis equalizers, specifically MLP and RBF equalizers.

In this paper, a novel method to reduce additive time-varying noise is proposed. Unlike the previous methods, the proposed method requires neither the assumption about noise nor the estimate of the noise statistics from any pause regions. The enhancement is performed on a band-by-band basis for each time frame. Based on both the decision on whether a particular band in a frame is speech or noise dominant and the masking property of the human auditory system, an appropriate amount of noise is reduced in time-frequency domain using modified spectral subtraction. The proposed method was tested on various noisy conditions: car noise, F16 noise, white Gaussian noise, pink noise, tank noise and babble noise. On the basis of segmental SNR, inspection of spectrograms and MOS tests, the proposed method was found to be more effective than spectral subtraction with and without pause detection in reducing noise while minimizing distortion to speech.

A communication model and a computer assisted communication method are introduced. With this model incorrect communications between humans are explained and then a method to lead successful communications with computer is illustrated. This method improves qualities of communications and can be applied to co-operative works. On the basis of the communication method, we have been developing a co-operative visual software requirements definition method via network with a visual requirements language named VRDL. Our method will improve quality of software requirements specification (SRS).

System specifications should be refined to meet stakeholders' requirements as much as possible, because the first specification does not satisfy all stakeholders in general. This paper presents a procedure to refine behavioral specification to satisfy stakeholders. Non-functional requirements are used for checking stakeholders' satisfaction. With this procedure, stakeholder-dissatisfaction can be reduced and new possibilities to satisfy or dissatisfy other stakeholders can be found, since a modification to cancel dissatisfaction can sometimes influence the satisfaction of the others.

We propose a set of Fabry-Perot etalons integrated in a planar lightwave circuit (PLC-FPE) designed for a unified system for broadcasting and communication. A PLC-FPE containing four etalons having different cavity lengths is fabricated and their loss and frequency characteristics are investigated. The total loss and the maximum finesse were found to be 8 dB and 34, respectively.

At high-level synthesis for system VLSIs, their power consumption is efficiently reduced by applying gated clocks to them. Since using gated clocks causes the reduction of power consumption and the increase of area/delay, estimating trade-off between power and area/delay by applying gated clocks is very important. In this paper, we discuss the amount of variance of area, delay and power by applying gated clocks. We propose a simple gate-level circuit model and estimation equations. We vary parameters in our proposed circuit model, and evaluate power consumption by back-annotating gate-level simulation results to the original circuit. This paper also proposes a conditional expression for applying gated clocks. The expression shows whether or not we can reduce power consumption by applying gated clocks. We confirm the accuracy of proposed estimation equations by experiments.

Due to large capacitance, high access ratio and wide access bitwidth, frame memory is one of the most energy consuming devices in modern video encoders. This paper proposes a new architectural technique to reduce energy dissipation of frame memory through adaptive bitwith compression. Unlike related approaches, the technique utilizes the fixed order of memory accesses and data correlation of video sequences, by dynamically adjusting the memory bitwidth to the number of bits changed per pixel. Instead of treating the data bits independently, we group the most significant bits together, activating the corresponding group of bit-lines adaptively to data variation. The approach is not restricted to the specific bit-patterns nor depends on the storage phase. It works equally well on read and write accesses, as well as during precharging. Simulations show that using this method we can reduce the total energy consumption of the frame memory cell array by 20% without affecting the picture quality. The implementation scheme is simple yet compact.

In modern high-capacity wavelength division multiplexing (WDM) transmission systems, there is increasing demand for large transmission capacity. To achieve this purpose, an L-band (1565-1625 nm) erbium-doped fiber amplifier (EDFA) is very effective method because the conventional silica-based EDF can be used. In EDFAs that used in WDM transmission systems, the gain flatness of EDFA is very important. A passive gain equalizer flattens the gain profile of EDFA. But the gain flatness in L-band deteriorates due to dynamic gain-tilt (DGT) and temperature gain-tilt (TGT) when the operating condition of the EDFA changes, while the EDFAs should maintain the gain flatness even if the operating condition has changed. To solve this problem, we propose an active gain-slope compensation technique for the L-band EDFA using a thulium-doped fiber (TDF). The EDFA actively gain-slope compensated by the TDF compensator keeps the gain profile constant for the wide input power range of more than 8 dB, a wide temperature range of 65 without gain-tilt in a wavelength band between 1575 nm and 1610 nm. Furthermore, the EDFA keeps a low noise figure of less than 7.5 dB.

An adaptive hybrid acquisition system is presented. The proposed system combines an antenna diversity technique and the cell-averaging constant false alarm rate (CA-CFAR) algorithm to acquire a pseudo-noise (PN) sequence for code-division multiple-access (CDMA) systems. Since conventional acquisition systems have a fixed threshold value, they are unable to adapt to varying mobile communications environments, resulting in a high false-alarm rate or low detection probability. Accordingly, an antenna diversity technique and adaptively varying threshold scheme using the CA-CFAR algorithm are applied to improve the detection performance. Based on deriving the detection probability, false alarm rate, miss detection probability, and mean acquisition time in Rayleigh fading channels, the performance of the proposed system is compared to that of a conventional system with a fixed threshold.

Network traffic characteristics impacts directly network performance, and resource allocation policies. In this work, we introduce a multi-agent system, that manages the performance of web servers with minimal cost of mirroring. In our proposed system each web server is viewed as a software agent that perceives its environment by monitoring its traffic. The goal of the agent is to manage the performance, using cooperative mirror servers, while minimizing the cost of mirroring. Communication between the agents enables each web server to decide about its future actions, which is whether to share its load with the cooperative mirror servers, and how much load to assign to them. The architecture of a software agent that is intended to manage the performance of a web server, is elaborated and its different modules are described. Also a set of cooperative agents is defined, that form a multi-agent system and is intended to assure maintaining the performance with minimal cost of mirroring. The experimental results presented in this article illustrates the effectiveness of the proposed system.

This paper proposes a quasi-coherent equivalent-time sampling method to acquire repetitive wideband waveform signals with high throughput. We have already proposed a new sampling system which incorporates the pre-trigger ability and the time jitter reduction function for a fluctuated input signal while maintaining the waveform recording efficiency. The quasi-coherent sampling method proposed in this paper can be adopted to it in order to improve its data acquisition throughput significantly. Numerical simulation results show effectiveness of our proposed method.

In this paper, a CMOS data recovery PLL for DVD-ROM is described. Some techniques have been introduced to alleviate the specifications required to analog circuits. A new phase detector alleviates the timing specification of a delay line and a pulse generator. A new frequency detector increases the capture range up to 8% of the center frequency. We have achieved to realize the data recovery PLL that operates at DVD-ROMx14 speed.

We have designed a demultiplexer (DMUX) with a simple structure, high-speed operation circuits and large bias margins. By using a binary-tree architecture and clock-driven circuits, multi-channel DMUXs can be constructed easily from the same elemental circuits, i.e., 1-to-2 DMUX, consisting of a T-FF and a 1-to-2 switch. By applying cell-level optimization and Monte Carlo simulation, bias margins and operation frequency of the circuits were enlarged. Logical operations of the 1-to-2 DMUX and a multi-channel DMUX, e.g., a 1-to-4 DMUX were experimentally confirmed. It was also confirmed that the large margins, 33% of the DMUX (1-to-2 switch) was kept up regardless the degree of integration, and that the 1-to-2 DMUX can operate up to 46 GHz by using measure of average voltages across Josephson junctions.

Previous device models for Hot Electron Bolometers (HEB) apply a lumped element approach to calculate the small signal parameters. In this work, large signal parameters are calculated using a nonlinear one-dimensional heat balance equation including critical current effects. Small signal equivalents are obtained by solving a linearized heat balance for the small signal beat term in the HEB. In this model, the absorbed bias power density is treated as a profile along the HEB bridge and the electrothermal feedback acts differently on different parts of the bridge. This model predicts more realistic conversion gain figures being about 10 dB lower than in previous ones.

Achieving optimal performance with minimal complexity are conflicting problems encountered in constructing receivers. In this paper, to solve the problem, we propose sector beamed space hopping which utilizes a Viterbi equalizing receiver. Reduction of the number of RF circuit sets, system complexity and decreasing the computational burden of the Viterbi equalizer through the use of sector beamed space hopping is presented. This is achieved using a sector beamed antenna which limits the number of paths in the multipath channel environment. This paper describes each key component which comprises the system and discusses the application of FH-SS communication. The channel is assumed to be an industrial indoor propagation channel, such as those found in a factory, where high reliability is required and many complex multipaths exist. We confirm through simulation that Viterbi equalization using less computational complexity can be obtained. It is found that there exists a trade off between system complexity and performance. Through the discussion of power consumption, cost and BER performance, we show that the proposed system achieves acceptable performance while having a low system complexity.

We report the measurements on the ramp-edge type Josephson and quasiparticle tunnel junctions with the different interface angle geometry using high-Tc YBa2Cu3O7-y (YBCO) electrodes. The YBCO/I/Ag tunnel junctions with different crystal-interface boundary angles are fabricated for the investigation of zero bias conductance peak. The angle dependent zero bias conductance peak typical to a dx2-y2-wave superconductor is observable. For Josephson junctions, YBCO ramp-edge junctions with different ab-plane electrodes relatively rotated by 45are fabricated using a CeO2 seed-layer technique. The temperature dependence of the maximum Josephson current for YBCO/PBCO/YBCO junctions (PBCO: PrBa2Cu3O7-y) exhibits angle-dependent behavior, qualitatively different from the Ambegaokar-Baratoff prediction. Under microwave irradiation of 9 GHz, the Shapiro steps appear at integer and/or half integer multiples of the voltage satisfying Josephson voltage-frequency relation, whose behavior depends on the sample angle geometry. The results are reasonably interpreted by the dx2-y2-wave theory by taking the zero energy state into account.

Lymph-node detection system using a high Tc SQUID and ultra-small particles was proposed. Pseudo lymph nodes containing small iron particles were made and the magnetic signal was measured. The SQUID signal was proportional to the weight of the iron in the fluid. At the distance of 20 mm, the detectable minimum weight of the iron was 40 µg. We demonstrated that the possibility of the application of the system to the human body.